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Late Pleistocene Glyptodont and Pampathere from Sonora, Mexico 439
Late Pleistocene (Rancholabrean) Glyptodont and Pampathere
(Xenarthra, Cingulata) from Sonora, Mexico
Jim I. Mead1,2,*, Sandra L. Swift1, Richard S. White3,
H. Greg McDonald4, and Arturo Baez5
1 Laboratory of Quaternary Paleontology, Quaternary Sciences Program, Northern Arizona University, Flagstaff, AZ 86001 USA.
2 Department of Geology, Northern Arizona University, Flagstaff, AZ 86001 USA.
3 International Wildlife Museum, 4800 W Gates Pass Road, Tucson, AZ 85745 USA.
4 National Park Service, 1201 Oakridge Dr. 250, Fort Collins, CO, 80525 USA.
5 College of Agriculture and Life Sciences, University of Arizona, Tucson, AZ 85721 USA.
* James.Mead@nau.edu
ABSTRACT
The fossil-rich deposits of Térapa (east-central Sonora) contain more than 60 zoological taxa,
many with tropical affi nities such as Crocodylus (crocodylian), Hydrochaeris (capybara), and many
birds. The deposits also contain the dermal ossicles (osteoderms) of two extinct xenarthrans, a glyptodont
(Glyptotherium cylindricum) and a pampathere (giant armadillo; Pampatherium cf. mexicanum).
Glyptodont remains are also known from other less-well studied localities in Sonora. The faunas from
these localities also contain the genus Bison, which indicates that the deposits are of the Rancholabrean
Land Mammal Age, late Pleistocene. The presence of Pampatherium at Térapa and the presence of
Glyptotherium at Térapa and the Río Mayo/Río Yaqui sites represent the fi rst published accounts of these
species from Sonora, and greatly extends their known geographical distribution during the Rancholabrean
by about 1,100 km into northwestern Mexico.
Key words: Xenarthra, pampathere, glyptodont, Rancholabrean, Pleistocene, Sonora, Mexico.
RESUMEN
Los yacimientos ricos en fósiles de Térapa (área centro-oriental de Sonora) contienen más de
60 taxon zoológicas, muchos con afi nidades tropicales como Crocodylus (crocodrilo), Hydrochaeris
(capibara), y muchas aves. Los depósitos contienen además la dermis ósea de oído (osteodermis) de dos
xenartros extintos, un gliptodonte (Glyptotherium cylindricum) y un armadillo gigante (Pampatherium cf.
mexicanum) (Mammalia, Xenarthra). También se han hallado restos de gliptodonte en otras localidades
de Sonora menos estudiadas. Las faunas de estas localidades contienen además el género Bison, lo cual
indica que los depósitos son del Rancholabreano (Rancholabrean Land Mammal Age), Pleistoceno tardío.
La presencia de Pampatherium en Térapa y de Glyptotherium en Térapa y los sitios del Río Mayo/Río
Yaqui representa el primer recuento publicado de estas especies en Sonora y extiende grandemente su
distribución conocida durante el Rancholabreano, o pleistoceno tardío, en unos 1,100 kms hacia el
noroeste de México.
Palabras clave: Xenartra, pampaterio, gliptodonte, Rancholabreano, Pleistoceno, Sonora, México.
Revista Mexicana de Ciencias Geológicas, v. 24, núm. 3, 2007, p. 439-449
Mead et al.
440
INTRODUCTION
Members of the mammalian order Xenarthra comprise
a prominent part of the South American fauna. Most of the
evolutionary history of the group occurred on that continent,
yet by the late Miocene some members dispersed over the
emerging Panamanian land bridge of Central America to
populate Mexico, the United States, and portions of Canada
(Webb and Rancy, 1996). This dispersal was part of the
Great American Biotic Interchange (GABI) of Neotropical
and Nearctic taxa. As recorded in the North American fos-
sil record, it occurred primarily during the latest Miocene
(early Hemphillian Land Mammal Age (LMA); 9-7 Ma)
and continued intermittently through the late Pliocene to
early Pleistocene (late Blancan LMA and early Irvingtonian
LMA; 2.7-1.0 Ma) (Morgan, 2005).
Living and extinct members of each of the two sub-
orders of xenarthrans, the pilosans (sloths and anteaters)
and cingulates (armadillos, pampatheres, and glyptodonts)
(McDonald, 2002) are known from Mexico. Representatives
of these suborders dispersed during the GABI. Knowledge
about the evolutionary history and distribution of these taxa
has been based primarily on fossils from the United States.
The records of fossil xenarthrans in Mexico are less exten-
sive and inadequately understood as compared to those in
the United States, and the review of xenarthran fossils by
McDonald (2002) clearly illustrated a latitudinal bias to the
known distribution. This is unfortunate as the geographic
position of Mexico represents today the northern extension
of the Neotropics and the southern extension of the temper-
ate climates and biotic communities of the Nearctic. The
northern state of Sonora represents this critical boundary
between the two biomes, a zone that shifted north and south
with the pulsating changes of glacial and interglacial climate
changes during the Pleistocene.
Although many xenarthrans were present in North
America during the Neogene, some apparently were re-
stricted to the environments of Mexico and did not venture
into the temperate United States. The record of xenarthrans
from Mexico is intriguing yet clearly insuffi ciently studied
to permit adequate statements about distribution patterns and
dispersal routes relative to chronology and environmental
change. Any evidence, especially from the northern portion
of Mexico, is signifi cant and of biogeographic and envi-
ronmental importance. Of interest here are the cingulates,
which include three subgroups: Dasypodidae (living and
extinct armadillos), Pampatheriidae (extinct pampatheres or
giant armadillos), and Glyptodontidae (extinct glyptodonts).
The earliest record of cingulates in Mexico is from early
Blancan deposits in the state of Guanajuato. Pampatheres
are represented there by the genus Plaina in deposits
dated between 4.7 and 4.8 Ma, and for the glyptodonts by
Glyptotherium from layers dated between 3.9 and 3.1 Ma
(Flynn et al., 2005). Here we report remains of glyptodonts
and pampatheres from the deposits at Térapa in east-central
Sonora and other less studied localities within the state.
Today the only xenarthran to inhabit Sonora is the nine-
banded armadillo (Dasypus novemcinctus, Dasypodidae),
which lives in southern-most portion of the state at Alamos
(Mendoza-Durán, 2005).
FOSSIL LOCALITIES IN SONORA
Térapa
The fossil-rich deposits of Térapa contain more than
60 zoological taxa, many with tropical affi nities such as
Crocodylus (crocodylian) and Hydrochaeris (capybara),
along with many birds and Bison (bison) (Mead et al.,
2006). Carranza-Castañeda and Roldán-Quintana (2007)
briefl y mention their recovery of surface fi nds of Bison
and Equus (horse) from Térapa. Térapa is located along the
Río Moctezuma in interior east-central Sonora (Figure 1;
29º 41’ N latitude; 109º 39’ W longitude, 605 m elevation).
The Río Moctezuma joins the Río Yaqui and enters the
Gulf of California (28ºN, 111ºW), positioning Térapa 350
km inland. The geological context and stratigraphy of the
deposits at Térapa are described in Mead et al. (2006). A lava
fl ow within the Moctezuma volcanic fi eld described by Paz-
Moreno et al. (2003) created at least one catchment basin
approximately 1 by 2 km adjacent to the Río Moctezuma.
Bison teeth and post-cranial remains recovered by Mead et
al. (2006) from throughout the 11 m of stratifi ed sediments
prescribe an assignment for the deposit and encased fauna
to the Rancholabrean (RLB) LMA of the late Pleistocene
(see Bell et al., 2004).
All fossil specimens from Térapa are temporarily
archived into the Laboratory of Quaternary Paleontology,
Quaternary Sciences Program, Northern Arizona University
(NAU QSP), Flagstaff, Arizona, USA. Within this system,
all specimens are curated into a numbering classifi cation
specifically for Térapa (TERA) and eventually will be
returned to Sonora.
The cingulate remains from Térapa come from the
lowest As1/As2 sediments that represent the initial fi lling of
the basin and from the lower (Bp1) and upper (Bp2) marsh
units (Mead et al., 2006). Although it is not yet understood
how much time it took to fi ll the basin with 11 meters of
sediments and fossils, it is apparent that cingulates utilized
the local environments throughout the depositional history
of the catchment.
Río Mayo / Río Yaqui Localities
Howard Scott Gentry traveled extensively throughout
northwestern Mexico in the 1930s where he recorded fossil
deposits, as well as the modern vegetation. Although his
contributions about the vegetation are well published (see
references in Martin et al., 1998), his fossil discoveries are
less well known, mostly unpublished, and documented by
Late Pleistocene Glyptodont and Pampathere from Sonora, Mexico 441
May 10th, 1936, based on his plant collecting notes in the
Herbarium at the University of Arizona. La Botana is located
at approximately 490 m altitude and is about 10 km. west of
the town of Tesopaco. (Figure 1). The site is located close to
the divide between the Río Yaqui and Río Mayo drainages,
which are not clearly delineated on available maps. Gentry,
in a letter to the Frick Lab, also indicates that it is in the Río
Yaqui drainage. Martin et al. (1998) also thought that the
site was likely in the Río Yaqui drainage
Fossils were abundant and included Glyptotherium
in association with Bison, which indicates a RLB age for
the deposits. Gentry also recovered Equus, Camelops,
Mammuthus, and Odocoileus. Fossils were removed from
an ‘argillaceous lime’ unit. Brief site descriptions and a
map of collecting localities are recorded in Gentry’s fi eld
notes submitted to C. Frick, June 1, 1937. The locality was
visited on March 23, 1975 by Paul S. Martin and one of
his students, Geoff Spaulding (both then at the University
of Arizona, Desert Laboratory, Tumamoc Hill, Tucson,
Arizona). They made a small collection of vertebrate fos-
sils (Martin, pers. com.). Fossil recovered by the UA party
include the Glyptotherium osteoderms documented below,
and Equus, Bison, and cf. Capromeryx. Specimens from
La Botana are curated at NAU QSP (via the University of
fi eld notes and letters to Childs Frick (Gentry and Hadley,
1995:237-243). These letters and notes are archived in the
Department of Paleontology, American Museum of Natural
History (AMNH), New York. The materials collected by
Gentry in Sonora are preserved in the vertebrate paleon-
tology collections at the AMNH. We have examined these
briefl y, but have not produced a detailed analysis. Only
those localities with remains of cingulates are presented
here. Clearly, additional studies of these fossil localities
are greatly desired; we plan further study of Gentry’s
Rancholabrean material from Sonora.
La Botana
Gentry described three localities from the vicinity
of Tesopaco: 1) 8 km southeast, 2) 16 km west and north,
and 3) 25 km west and north. Gentry’s fi eld notes for his
fi rst few weeks in this area are confusing. It appears likely
that his Tesopaco Locality 1 is what he later called Los
Coyotes, that Tesopaco Locality 2 is probably La Botana,
and that Tesopaco Locality 3 is Llano Prieto (the latter two
are described below).
Gentry fi rst visited La Botana between May 5th and
Figure 1. Map of Mexico and adjacent USA showing distribution of Glyptotherium (open square) from Gillette and Ray (1981) and McDonald (2002) and
Pampatherium (dot) from McDonald (2002) in relationship to the locations of Térapa, the Río Mayo/ Río Yaqui deposits, and La Brisca (open triangle)
from Van Devender et al., (1985). More detailed discussion about locations can be found in the text and in Mead et al. (2006).
Mead et al.
442
Arizona, Laboratory of Paleontology, Tucson) and in the
collections at the AMNH.
Llano Prieto
The Llano Prieto fossil locality is located north of La
Botana, up the headwaters of the Río Cedros, a tributary of
the Río Mayo. As noted below, Llano Prieto was originally
referred to as Tesopaco 3 by Gentry. An ‘argillaceous lime
and gravel’ unit with fossils is located about 6 m below
surface. Bison and an unverifi ed record of Glyptotherium
were recovered together from the locality, and indicate a
RLB age for the remains. Data is recorded in H. S. Gentry’s
fi eld notes submitted to C. Frick, June 1, 1937. We have not
been able to locate a specimen of Glyptotherium from this
locality in the AMNH collections.
Chinobampo
The site of Chinobampo is located along the Arroyo
Chinobampo, which appears to drain northwards into the
Río Mayo, and is about midway between Navajoa and
Alamos. The settlement of Chinobampo is shown on the
Mexican Topographic Map (1:50,000) Masiaca G12B56.
Some older maps show a ranch named ‘Agua China’ in
the same area. According to Gentry, ‘Chinobampo’ means
‘Chinaman Well’. Since the word “chino” locally also
means the tree palo chino (Havardia mexicana), Martin
et al. (1998) translate the place name as “Chino in the wa-
ter”. The site was mentioned briefl y in Aveleyra Arroyo de
Anda (1964) and is notable for having produced a human
skull and some fragmentary postcranial remains, possibly
from the same layers that produced the Rancholabrean
fossil mammals. Gentry discovered the site January 10,
1937 (based on both a geological report written by John
C. Blick (another one of Frick’s collectors) and submitted
to Frick December 13, 1937, and Gentry’s plant collecting
notes in the Herbarium at the University of Arizona. Blick
and Gentry returned to Chinobampo in March of 1937 at
Frick’s request to make an intensive examination of the
geology. The geologic situation at Chinobampo appears
to be very similar to that described for Tèrapa, Sonora,
by Mead et al. (2006). A basalt fl ow dammed the arroyo,
causing an impoundment in which sediments consisting of
‘argillaceous lime, lime, and black lime’ were deposited.
Blick lists the following fossils in his notes: a palate of a
large species of Camelops, a horse skull (Equus), and the
partial skeleton of a Canis sp. (wolf). The ‘wolf’ skeleton is
listed in the Frick Laboratory receiving notes as ‘cat.’ The
same receiving notes list a Bison sp. mandible fragment and
four glyptodont osteoderms. A RLB age is assigned based on
the recovery of Bison with extinct species. Specimens from
Chinobampo are curated in the Department of Paleontology,
AMNH.
SYSTEMATIC PALEONTOLOGY
Order Xenarthra Cope, 1889
Suborder Cingulata Illiger, 1811
Superfamily Glyptodontoidea Gray, 1869
Family Glyptodontidae Gray, 1869
Genus Glyptotherium Osborn, 1903
Glyptotherium cylindricum (Brown) Gillette and
Ray, 1981
Fossil material. Osteoderms (dermal ossicles) assigned
to Glyptotherium cylindricum include:
Térapa— TERA-25, 27-30, 50: interior carapace
osteoderms; TERA-24, 49: lateral osteoderms near border;
TERA-26, 31: caudal border carapace osteoderm; TERA-
32-36, 45-48: conical osteoderms; TERA-37-44: anterior
osteoderm of caudal ring: TERA-51: large section of cara-
pace from single individual.
La Botana— NAU QSP-17887: one mid-carapace
osteoderm; NAU QSP-17886: one lateral border osteoderm;
AMNH 59592 and 59693: 163 isolated and 6 articulated
osteoderms; AMNH 59594: two mid-carapace osteoderms;
AMNH 96369: one mid-carapace osteoderm.
Llano Prieto— Mentioned in fi eld notes; no osteo-
derms were observed in the AMNH collections.
Chinobampo— Four mid-carapace osteoderms:
AMNH 59595. Only the ventral side of these osteoderms
is preserved. The dorsal side is obscured with a thick coating
of caliche-like carbonate.
Remarks and identifi cation. North American glyptodonts
are distinct from the South American forms and placed in
their own genus Glyptotherium, which is closely related to
the South American genus Glyptodon (Gillette and Ray,
1981). The earliest glyptodont in Mexico, Glyptotherium
sp., is recorded from early Blancan deposits in central
Mexico (Carranza-Castañeda and Miller, 2004). There are
three recognized species of Glyptotherium from Mexico:
G. cylindricum [Rancholabrean LMA; one locality], G.
fl oridanum [Rancholabrean LMA; two localities], and G.
mexicanum [Rancholabrean LMA; one locality] (Gillette
and Ray, 1981; McDonald, 2002). Additional species are
described and are restricted to the United States and older
deposits (G. arizonae [Irvingtonian LMA] and G. texanum
[Blancan LMA]).
The distribution of the genus was more extensive
during the Blancan and Irvingtonian with remains occur-
ring in Arizona and New Mexico respectively (Morgan and
Lucas, 2005; Morgan and White, 2005; White and Morgan,
2005), and even north into Oklahoma (Czaplewski, 2004).
Records of late Pleistocene, RLB, Glyptotherium in the
United States are concentrated along the Gulf States region
(Gillette and Ray, 1981). Consequently from the Blancan to
the Rancholabrean there was a reduction in the range of the
genus to the east and south in the United States. Extensive
Late Pleistocene Glyptodont and Pampathere from Sonora, Mexico 443
a)
b)
c)
fi eld studies have shown that no Rancholabrean records of
Glyptotherium exist in the Southwest United States (Mead
et al., 2005; Morgan and Lucas, 2005). Until now its distri-
bution in Mexico during the Rancholabrean was thought to
be restricted to central and southern portions of the country
(McDonald, 2002; Figure 1).
The dermal armor of glyptodonts is their single most
outstanding characteristic. Consequently the morphology of
the osteoderms has long been recognized as taxonomically
important. Each osteoderm that covers the body region
(carapace) is polygonal (six- or four-sided) and is tightly
sutured to its neighbors, inhibiting trunk mobility. For
a discussion of the development of the osteoderms, see
Holmes and Simpson (1931) and Hill (2006). The typical
hexagonal osteoderm has a central figure and several
peripheral figures symmetrically arranged around the
center, producing a characteristic and diagnostic rosette
pattern (terminology of Hill, 2006). Identifi cation characters
used here follow Gillette and Ray (1981). In G. texanum,
the central figure is larger than the peripherals, and is
convex and slightly raised above the level of the fl attened
peripheral fi gures. In G. arizonae and G. cylindricum, the
central fi gures are relatively smaller than the peripherals,
not greater than 50 percent of the entire osteoderm diameter,
and are generally fl at to weakly convex. In G. fl oridanum
the central fi gure is approximately equal in size to those of
the peripherals, and is typically raised and weakly concave.
The central fi gure on the osteoderms of G. mexicanum is
generally large, never smaller than half (50 percent) of the
osteoderm diameter.
Although seemingly distinct for all the species, we
recognize that there is variation of the rosette size and pat-
tern within and among species. Isolate osteoderms may be
diffi cult to accurately identify in all cases. Complicating
this is the fact that G. cylindricum and G. mexicanum are
less than adequately understood, being known only from
the type localities (Carranza-Castañeda and Miller, 1987;
McDonald, 2002). Better material may show that these
two taxa are synonomous. Until more complete carapaces
of Glyptotherium from Mexico are studied in detail and
apomorphies established for the osteoderms, we identify
our specimens from Sonora using the characters outlined
above from Gillette and Ray (1981). In addition, we omit
G. arizonae and G. texanum from consideration of the
Rancholabrean glyptodonts based on their earlier age as-
signment. Clearly much remains to be understood about
Mexican glyptodonts.
TERA-24 measures 39.6 by 34.8 mm. The thickness
varies from 11.2 to 12.6 mm which indicates that the os-
teoderm is from a lateral, near-border location (Figure 2a).
Due to location on the carapace, the TERA-24 specimen
does not have the typical rosette pattern.
TERA-25 is a typical rosette osteoderm of the mid-
carapace (Figure 2b). Overall the osteoderm measures 37.4
by 45.1 mm, and is 16.3 mm in thickness. The central fi gure
of the rosette measures 16.6 mm (36 percent of the greatest
diameter). The central fi gure is fl at and only slightly larger
than the peripheral fi gures, consistent with the pattern found
on G. arizonae and G. cylindricum (Gillette and Ray, 1981).
The above character would imply that the Glyptotherium
from Térapa is more similar to G. cylindricum than to G.
mexicanum. We use this solitary character to identify the
fossil glyptodonts to species, omitting the posibility of
G. arizonae based on age assignment. Additional interior
carapace osteoderms have the typical rosette pattern with
the central fi gure relatively small: TERA-27 (52.4 by 41.4
mm; 17.5 mm thick; central fi gure is 15.2 mm wide (29
percent of the diameter) and slightly depressed; TERA-29
(40.1 by 39.1 mm; 16.4 mm thick; central fi
gure is 16.7
Figure 2. Osteoderms of Glyptotherium cf. G. cylindricum from Térapa.
a: TERA-24; b: TERA-25; c: TERA-26. Scale is 10 mm.
Mead et al.
444
mm wide (42 percent of the diameter); TERA-30 (42.1 by
33.4 mm; 17.5 mm thick; central fi gure is 18.9 mm wide
(45 percent of the diameter); and TERA-50 (38.5 by 37.3
mm; 16.3 mm thick; central fi gure is 16.6 mm wide (43
percent of the diameter).
TERA-26 is a large osteoderm (53.9 by 48.5 mm) that
appears to be from the second row of osteoderms adjacent
to the border osteoderms along the caudal edge of the
carapace (Figure 2c).
TERA-51 is a 1.5m-long section of the carapace from
a single individual Glyptotherium (Figure 3). Some of the
osteoderms have the internal surface oriented up while
others have the external surface oriented up indicating that
sections of both the left and right side of the carapace are
preserved or that some were fl ipped over during burial. Four
osteoderms were measured: 35.0 by 41.8 mm (central fi gure
is 16.1 mm, or 38 percent of the diameter), 35.8 by 39.9 mm
(central fi gure is 15.9 mm, or 44 percent of the diameter),
40.9 by 37.3 mm, and 35.5 by 29.6 mm. The relative size of
the central fi gures from this carapace section indicates that
this specimen can also be referred to G. cylindricum.
The remains from La Botana include a small lateral
border fragment (NAU QSP-17886) and a mid-carapacial
osteoderm (NAU QSP-17887). The latter osteoderm is
more complete and has a maximum diameter of 48.4 mm
and a thickness of 20.1 mm. The central fi gure measures
19.8 mm. While the margin of the osteoderm is somewhat
broken, enough remains that we are confi dent that our meas-
urements are good approximations. In any case, a slightly
larger maximum diameter would only serve to decrease the
ratio of the diameter of the central fi gure to the maximum
diameter of the osteoderm. As preserved, the central fi gure
is 40.9 percent of the osteoderm diameter, placing it well
within the range recorded for Glyptotherium cylindricum
and well below the minimum for G. mexicanus.
The 12 best preserved osteoderms from La Botana
(Tesopaco Locality 2) in the AMNH (59592, 59593 and
96369) gave an average maximum diameter of 51.6 mm
(46.8 – 58.9), an average length of the central fi gure of
20.5 mm (18.1 – 21.9), with the central fi gure averaging
39.8 percent (33.6 – 45.2) of the osteoderm diameter.
These osteoderms are also well within the range report-
ed for G. cylindricum and well below the minimum for
G. mexicanus.
We have examined the osteoderms in the AMNH from
Chinobampo and confi rm their identity as Glyptotherium.
However, the dorsal surface is encrusted with a caliche-like
carbonate which obscures the sulci and makes measuring
the central fi gure inaccurate.
Superfamily Glyptodontoidea Gray, 1869
Family Pampatheriidae Paula Couto, 1954
Genus Pampatherium Gervais and Ameghino, 1880
Pampatherium cf. P. mexicanum Edmund, 1996
Fossil Material. Remains assigned to Pampatherium
include isolated imbricating and buckler osteoderms
(TERA-18-22).
Figure 3. A series of in situ, exposed osteoderms of Glyptotherium cf. G. cylindricum from a single section of carapace (TERA-51) from Térapa. Both
internal and external faces of osteoderms are showed. Scale is 100 mm.
Late Pleistocene Glyptodont and Pampathere from Sonora, Mexico 445
a)
b)
c)
curs on TERA-20 and it is not depressed; the central fi gure
is fl attened and devoid of a keel or boss (Figure 4b). These
combined characters indicate that TERA-19 and 20 belong
to the genus Pampatherium and not Holmesina, although
both taxa are known from Mexico.
TERA-22 is relatively small (21.6 by 19.3 mm) with
a generally ovoid shape. It has only the slightest presence
of follicular pits along the margin, and may represent a
cephalic osteoderm. Although the specimens appear similar
to those described as P. mexicanum (Edmund, 1996) we
only tentatively ascribe the specimen to this species until
a more complete carapace or collection of osteoderms is
recovered from Térapa.
Remarks and identifi cation. Pleistocene pampatheres are
represented by seven species in two genera: Holmesina and
Pampatherium. McKenna and Bell (1997) synonymized
these genera without comment; we retain the two genera
here. The osteoderms provide one mechanism for distin-
guishing these taxa (Edmund, 1996; Scillato-Yané et al.,
2005). Each osteoderm in the carapace bears a pattern
refl ecting the ornamentation of its covering keratinous
osteoderm, which is distinctive for the genus and often for
the species (Edmund, 1985, 1987, 1996). The carapace of
all pampatheres has a mid-section consisting of three imbri-
cating bands of osteoderms. Anterior to these bands are the
pectoral buckler osteoderms and posterior to the bands are
the pelvic buckler osteoderms. All of these are distinct in
both ornamentation and size from the carapace osteoderms
found in the dasypodid armadillos (Edmund, 1985).
Buckler osteoderms from Pampatherium are weakly
ornamented (Figure 4b). The marginal band may be absent
(typical of the Mexican population) or may consist of a
narrow band of follicular pits on the posterior and lateral
margins; the marginal band is not signifi cantly depressed
below the submarginal band (Edmund, 1996). The central
portion of the buckler osteoderms in Pampatherium is broad
and low with no boss or raised keel (Edmund, 1996). In
contrast to those of Pampatherium and those recovered from
Térapa, Holmesina buckler osteoderms have a distinct, al-
most continuous depressed margin, one with a submarginal
band that is a clearly defi ned rectangle. The central region
typically is raised, often with a keeled boss (Edmund 1985,
1987, 1996; Scillato-Yané et al., 2005).
While three species of Pampatherium have been
described, only P. mexicanum is present in North America
(Edmund, 1996). Although the Térapa specimens appear
to match the holotype for that species, we take a conserva-
tive approach here and only tentatively assign our fossils
to species. The recovery of additional osteoderms or other
skeletal elements is needed to permit a more defi nitive
identifi cation.
TERA-18 is the anterior half of either an imbricating
osteoderm, or the anterior-most osteoderm of the pelvic
buckler (Figure 4a). It preserves the inclined surface over
which the osteoderm in front of it overlaps. The anterior-
most edge of TERA-18 has been broken so that the edge
is 5.3 mm in thickness. The osteoderm would match either
the C or D osteoderm of Edmund (1985).
TERA-20 is a complete buckler osteoderm that meas-
ures 42.5 mm long by 25.4 mm wide at the anterior end and
29.1 mm wide at the posterior end, and 8.4 mm in maximum
thickness (Figure 4b). TERA-20 is somewhat unusual in that
the osteoderm is wider at the posterior end; most buckler
osteoderms are either rectangular or slightly narrower at
the anterior end. TERA-19 is the anterior half of a buckler
osteoderm 24.6 mm wide and 7.2 mm in maximum thick-
ness (Figure 4c). Both buckler osteoderms are rectangular in
shape, lack the submarginal band and appear to have come
from the pelvic buckler. Only a slight follicular pit band oc-
Figure 4. Osteoderms of Pampatherium cf. P. mexicanum from Térapa. a:
TERA-18; b: TERA-20; c: TERA-19. Scale is 10 mm.
Mead et al.
446
DISCUSSION AND CONCLUSIONS
Distributions
Late Pleistocene Rancholabrean-age deposits are
common in Arizona and New Mexico, yet in adjacent north-
western Mexico (Sonora and Chihuahua) the published ac-
counts of such faunas are extremely rare. The few analyzed
Rancholabrean deposits and their faunas in Sonora either
date to the late Wisconsinan Glaciation (~< 80,000 years;
Arroyo-Cabrales et al., 2002) or possibly to the preceding
Sangamon interglacial (Van Devender et al., 1985). The
deposits at Térapa represent the most extensively studied
RLB deposits in Sonora, yet they may be of a different
radiometric age than the few other described faunas (Mead
et al., 2006). Until now, Glyptotherium and Pampatherium
dating to the RLB have not been reported from Sonora.
Miller and Carranza-Castañeda (2001) stated that the
understanding of the fossil fauna of Mexico has been greatly
enhanced through the investigations in central Mexico. As
was clearly stated by Arroyo-Cabrales et al. (2002), the fos-
sil history of northern Mexico is nearly void of information.
Figure 1 shows the known distributions of Glyptotherium
and Pampatherium. The presence of these taxa at Térapa
represents the fi rst published accounts of these species from
Sonora and greatly extends their known distributions during
the RLB into northwestern Mexico.
Glyptotherium of RLB age is found in central, eastern,
and Gulf Coastal Plain Texas and southeastern USA (pre-
dominantly Florida; Gillette and Ray, 1981). In Mexico,
Glyptotherium of RLB age is recorded from southeast-
ern Ciudad Delicias, Chihuahua (Silva-Bárcenas, 1969),
Cedazo, Aguascalientes (Mooser and Dalquest, 1975),
Ameca, Jalisco (Brown, 1912), and localities farther south
(McDonald, 2002; Figure 1). The Térapa and other Sonoran
localities fi rmly place Glyptotherium during the RLB at least
425 km farther west and 1,150 km farther north than previ-
ously recorded. Formerly, the farthest north occurrence of
Pampatherium during the RLB was in Jalisco (McDonald,
2002; Figure 1).
Environmental Setting
Térapa is situated today at the northern extent of the
subtropical thornscrub biotic community of the Neotropical
Realm (classifi cation of Brown et al., 1998). More precisely,
the local vegetation today is part of the Foothills Thornscrub
– a transition between the Sonoran Desertscrub and the
Tropical Deciduous Forest (which occurs in the foothills of
the Sierra Madre Occidental within 250 km of the Arizona
border). Summer rains and protection from deep winter frost
are essential for tropical biota (Martin and Yetman, 2000).
Today the northern limits of the Neotropics are in central
Sonora, with a relatively abrupt transition between 28° and
32° N latitude (Van Devender et al., 2000). Tropicality in-
creases from sea level inland into the foothills of the Sierra
Madre Occidental. The northern limit of the Neotropics is
not along the coast but inland where it approaches 28° 30’N.
The Foothills Thornscrub reaches farther north to within
about 100 km of the Arizona border in the Moctezuma and
Bavispe drainages (Van Devender et al., 1994). Térapa
is on a tributary of the Río Yaqui at 29º 41’ N (Figure 1).
Tropical species reach their northern limits by being effec-
tively ‘squeezed’ between the cold temperatures of higher
latitudes and the inadequate summer moisture found at
lower elevations (Martin et al., 1998; Martin and Yetman,
2000). It is this ‘edge-effect’ that shifted north and south
or up and down in elevation as climate, particularly rainfall
and temperatures, cycled through glacial and interglacial
regimes.
The recovered sediments, ostracodes, mollusks, and
vertebrates indicate that during the RLB local habitats at
Térapa included a slow moving stream, ponded water,
marsh, and submerged to emergent grasslands (Mead
et al., 2006). These authors inferred from the size of
the present Río Moctezuma valley that, during the late
Pleistocene, the setting permitted a well-developed riparian
corridor with tropical habitats that extended 350 km from
the coastal environments of the Gulf of California to the
interior location at Térapa. While the current imprecise
age assignment does not allow us to place the fauna from
Térapa within a particular Marine Isotope Stage, the fauna
which includes a crocodilian, capybaras, and most of the
recovered birds clearly indicate the presence of a subtropical
habitat farther north of its current boundary. A more precise
chronological analysis of the deposit is being conducted.
A precise chronology and environmental setting for
each of the three Río Mayo/Rio Yaqui localities of RLB
age is not yet available. However, tropical environments
currently extend up the drainage from the coast today, and
likely would have also done so during some or most climate
regimes during the Pleistocene. The Tropical Deciduous
Forest reaches about 1,000 m altitude within the drainage
(see Martin et al., 1998). We speculate that at least low
elevations along larger drainages, and the region of the
coast farther north of the Río Mayo, would have harbored
a robust tropical habitat during suitable Pleistocene climatic
regimes. What is not understood at present is whether or
not the required climate for the extension of tropical fl ora
and fauna to more northerly and /or more interior regions
occurred during a glacial or interglacial regime. Continued
detailed analysis of the Térapa locality, and our studies of
additional unpublished localities in Sonora, may hold the
answer to this and other questions.
Habitat Requirements
The habitat requirements for the extinct Glyptotherium
and Pampatherium are not fully known. As with the living
armadillos, the naked carapace on glytodonts and pam-
Late Pleistocene Glyptodont and Pampathere from Sonora, Mexico 447
patheres results in a high thermal conductance (McNab,
1978). The result is a smaller differential between body
temperature and the environment. Consequently, armadil-
los, and presumably glyptodonts and pamapatheres, despite
their larger size and improved body-mass to surface-area
ratio, would show a greater demand to increase metabolism
in order to maintain body temperature in response to small
changes in the ambient temperature. While Glyptotherium
fossils are known from farther north of Térapa into the
USA during the RLB, they are restricted to areas along
the Gulf of Mexico in the eastern portion of the continent.
Associated faunal elements in these regions imply a tropical
or at least subtropical habitat. It is also not yet determined
whether Glyptotherium and Pampatherium were tropical
obligates. This seems doubtful given the more northern
range of Glyptotherium. However, given the restricted
southern distribution of Pampatherium in North America in
comparison to Holmesina, and given that the other known
species of the genus are restricted to the tropics, it appears
more likely that Pampatherium was an obligate inhabitant
of tropical conditions.
We speculate that glyptodonts and pampatheres
lived in a habitat with abundant grass, and were grazers.
Webb (1978) included the Glyptotherium as one of nine
genera of savanna grazers that participated in the GABI.
In contrast, Gillette and Ray (1981) suggested that they
were likely “aquatic grazers” along with the capybaras.
Fariña (1995) questioned Gillette and Ray’s interpreta-
tion of Glyptotherium as having a preference for marshy,
lowland habitats based on a biomechanical analysis of
different South American genera of glyptodonts. The jaw
and dentition of Glyptotherium, as in other glyptodonts, is
well adapted for the processing of grasses. The jaw is deep
with extremely hypsodont, ever-growing teeth. The teeth
are among the most complex of any xenarthran teeth, being
trilobate with an arrangement of osteodentine in the center
to compensate for the lack of enamel, and the elongated and
massive zygomatic arch with a descending fl ange to orient
the masseter muscles to better grind abrasive vegetation such
as grasses (Ferigolo, 1985; Fariña, 1985, 1988).
In South America, all species of Pampatherium are
thought to be better adapted to extreme arid and semi-
arid environments than Holmesina (Scillato-Yané et al.,
2005). Based on a functional analysis of mastication in
Pampatherium, De Iuliis et al. (2000) concluded that among
the pampatheres, this genus was the most adept grazer of
resistant vegetation. Among the herbivorous cingulates, the
main differences in skull morphology refl ected the degrees
of vegetation coarseness they were capable of processing.
Such differences probably refl ected competitive exclusion
through niche partitioning within a shared biome or utiliza-
tion of different habitats (see Vizcaino et al., 1998). While
common in the Pampean region of Argentina, the range
of Pampatherium typum extended through Uruguay into
southern Brazil and west into Bolivia. Its widespread oc-
currence in this region is thought to refl ect its adaptation to
a more arid environment (De Iuliis et al., 2000). The other
species, P. humboldtii, is known from the more tropical
portions of South America, particularly northern and eastern
Brazil. Types of vegetation in these regions varied through
time. Vegetation during interglacial intervals resembled that
of the modern fl ora while, during glacial times there was
increased aridity, with large portions of the Amazon Basin
becoming savanna and cerrado habitat. The distribution of
P. humboldtii overlapped that of Holmesina paulacoutoi
in this region. This distribution refl ects the dynamics of
this changing habitat, and the two taxa may not have been
contemporaneous. They may have lived in the region alter-
natively, with Pampatherium being present during the times
when more arid savanna habitat predominated.
Although both Glyptotherium and Pampatherium
were recovered at Térapa along with other tropical elements,
there were also species in the fauna well adapted to a grass-
land/savanna habitat and more temperate climate, such as
Mammuthus, Equus, Camelops, and Bison. The ranges of
all these taxa also extend farther south of Térapa into central
Mexico so their presence at Térapa is not unexpected. The
distribution of Glyptotherium into the subtropical habitats
of the southeastern USA and its absence in Arizona or New
Mexico during the late Pleistocene RLB (Wisconsinan
Glaciation) would imply that this grazer required some sort
of tropical or subtropical element, including a permanent
water source in its habitat. The pampathere, Holmesina,
is known from eastern USA tropical habitats during the
Pleistocene, but never ventured west of the Texas coastal
region (Edmund, 1996). Pampatherium was not known
to have dispersed farther north than south-central Mexico
during the Pleistocene until it was found at Térapa. From
this distribution pattern, we conclude that Pampatherium
may have been a more tropical obligate than other South
American species within the genus and Glyptotherium.
The report here of Pampatherium and Glyptotherium
from RLB deposits in Sonora is unique and clearly illustrates
that much about the Pleistocene of northwestern Mexico is
only now beginning to be understood. More data is needed
to fully characterize the habitat, and to determine whether
the local plant community around Térapa during the RLB
was a grassland, a savanna, or a more closed community
with grass as an understory. Obviously the Neogene of
Sonora is in need of additional detailed fi eld and labora-
tory attention.
ACKNOWLEDGEMENTS
We thank Y. Petryszyn, P. Kresan, and C.V. Haynes
for their initial help with the project at Térapa. We also
appreciate assistance in the fi eld by E. Baez, A. Bair, T.
Bethard, V. Black, C. Bomberger, J. Bright, M.C. Carpenter,
J. Cruz, N.J. Czaplewski, G. Dean, F. and S. Duringer, P.
Gensler, M. Hollenshead, M. Imhof, R. Irmis, S. Jenkins,
C. Johnson, T. Joyal, A. Kelly, B. Long, C. McCracken, A.
Mead et al.
448
Mead, J. Meyers, G. Morgan, M. Palevich, W. Peachey, R.
Reppen, J. Toney, and G. Varhalmi. F. Tapia Grijalva and E.
Villalpando of Instituto Nacional de Antropología e Historia,
INAH Sonora, and J. Arroyo-Cabrales, Instituto Nacional
de Antropología e Historia, assisted with obtaining permits.
We thank H. Ruiz Durazo, S. Garcia Lopez, E. Maria Aruna
Moore, and many other people in the towns of Térapa,
Moctezuma, and El Llano for their continued support of our
project. We greatly appreciate the discussions and help from
N.J. Czaplewski, G. Morgan, P.S. Martin, E.H. Lindsay,
and C.J. Bell. We appreciate the continued discussions and
analyses on chronology, climate, and ostracodes from J.
Bright and D. Kaufman. We also appreciate the assistance
of Meng Jin, C. Norris, and S. K. Bell at the AMNH for
access to collections and to the records of Gentry’s fi eld
work which are contained in the Frick Archives. P. Jenkins
and R. Felger provided access to Gentry’s fi eld notes in the
Herbarium at the University of Arizona. We appreciate the
careful reviews of N.J. Czaplewski and T.R. Van Devender,
and the meticulous editing of C. White.
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Manuscript received: September 18, 2006
Corrected manuscript received: July 12, 2007
Manuscript accepted: August 10, 2007
